Blende 2.79a. Video Editing
Let's take some math.

12m with some seconds it is about 720 sec. Lets take this length. 

First video size =
bitrate * Length = 15112 Kb/s * 720s = 10880640 kb = 1360080 kB ~ 1.36 GB

Second video size = 
bitrate * Length = 26500 Kb/s * 720s = 19080000 kb = 2385000 kB ~ 2.38 GB


2.38GB - 1.36GB = 1.02GB!